1. Field of the Invention
The present invention is concerned with explosive shaped charges, and more particularly to an improved liner for use in such shaped charges and an improved shape charge which is especially useful in a well pipe perforating gun.
2. Related Art
The use of shaped charges for perforating the pipes or casings used to line wells such as oil and natural gas wells and the like, is well-known in the art. For example, U.S. Pat. No. 3,128,701, issued Apr. 14, 1964 to J. S. Rinehart et al, discloses a shaped charge perforating apparatus for perforating oil well casings and well bore holes.
The art has also devoted attention to providing a particular configuration of the shaped charge and its liner as shown, for example, in U.S. Pat. No. 5,221,808, issued Jun. 22, 1993 to A. T. Werner et al. The shaped charge therein disclosed includes the usual case, concave shaped explosive material packed against the inner wall of the case, and a metal liner lining the concave side of the shaped explosive. As disclosed in the paragraph bridging columns 3 and 4 of the patent, the taper is said to exist in the thickness of the liner 14 starting at the apex 18 thereof and ending with the skirt 16 thereof. At the first ten lines of column 4, specifications are given for the copper-bismuth liner 14 including a maximum variation in thickness along any given transverse section of the liner, a specified thickness of the skirt 16 of the liner 14, and the taper of the liner at the apex 18 and the skirt 16. It is not clear from the face of the patent precisely what is meant by the different specified "tapers" at the apex and the skirt.
Generally, shaped charges utilized as well perforating charges include a generally cylindrical or cup-shaped housing having an open end and within which is mounted a shaped explosive which is configured generally as a hollow cone having its concave side facing the open end of the housing. The concave surface of the explosive is lined with a thin metal liner which, as is well-known in the art, is liquified to form a jet of molten material upon detonation of the explosive and this jet of molten material exhibits a good penetrating power to pierce the well pipe, its concrete liner and the surrounding earth formation. Typically, the shaped charges are configured so that the liners along the concave surfaces thereof define simple conical liners with a small radius apex at a radius angle of from about 55.degree. to 60.degree.. Other charges have a hemispherical apex fitted with a liner of uniform thickness.
Generally, explosive materials such as HMX, RDX or HNS are mixed with binders such as wax or synthetic polymeric reactive binders such as that sold under the trademark KEL-F. The resultant mixture is cold- or hot-pressed to approximately 90% of its theoretical maximum density directly into the shaped charge case. The resulting shaped charges are initiated by means of a booster or priming charge positioned at or near the apex of the shaped charge and located so that a detonating fuse, detonating cord or electrical detonator may be positioned in close proximity to the priming charge.
The known prior art shaped charges are typically designed as either deep-penetrating charges or large-diameter hole charges. Generally, shaped charges designed for use in perforating guns contain 50 to 60 grams of high explosive and those designed as deep-penetrating charges will typically penetrate concrete up to about 12 inches. Large-diameter hole shaped charges for perforating guns create holes on the order of about one inch in diameter and display concrete penetration of up to about 9 inches. Such data have been established using API RP43, Section II test methods. Generally, typical disposable charges are not designed to withstand deep well pressures in excess of about 13,000 psi.